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Isoniazid (INH)

Prescription
Antimycobacterial (First-Line Anti-TB)
Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
1 available
Interactions
2 documented
Formulations
2

Mechanism of action

Prodrug activated by mycobacterial catalase-peroxidase (KatG) to form isonicotinic acyl radical which inhibits InhA (enoyl-ACP reductase), blocking mycolic acid synthesis — essential for mycobacterial cell wall. Bactericidal against actively growing M. tuberculosis.

At a glance

Class
Antimycobacterial (First-Line Anti-TB)
Schedule
Prescription
Storage
Store at room temperature, protect from light and moisture

Dosing

🐕

Dog

Used for M
Dose
10–20 mg/kg
Route
PO
Frequency
q24h
🐈

Cat

M
Dose
10–15 mg/kg
Route
PO
Frequency
q24h

Formulations

💊

Other — 2

Strength
—
Strength
—

Storage

Store at room temperature, protect from light and moisture

Safety

Monitoring parameters

Hepatic enzymes q2–4 weeks initially, then monthlyNeurological exam (neuropathy)CBCCulture response

Interactions

Major — 1

Phenobarbital
major
Isoniazid inhibits CYP enzymes metabolizing phenobarbital, increasing phenobarbital levels and toxicity. Isoniazid is also inherently hepatotoxic — additive liver injury risk.
Management: Monitor phenobarbital levels. Monitor hepatic enzymes closely. May need phenobarbital dose reduction.

Moderate — 1

Ketoconazole (Systemic)
moderate
Isoniazid may reduce ketoconazole absorption. Ketoconazole requires acidic gastric pH for dissolution — isoniazid may alter this.
Management: Separate by 2 hours. Monitor antifungal response.

Brands

Other markets

Nydrazid

FAQs

Frequently asked questions

›What is Isoniazid (INH)?
Isoniazid (INH) is a antimycobacterial (first-line anti-tb) used in pets. Prodrug activated by mycobacterial catalase-peroxidase (KatG) to form isonicotinic acyl radical which inhibits InhA (enoyl-ACP reductase), blocking mycolic acid synthesis — essential for mycobacterial cell wall. Bactericidal against actively growing M. tuberculosis.
›What is Isoniazid (INH) used for in pets?
Isoniazid (INH) is used in veterinary medicine for: Used for M; M.
›What is the Isoniazid (INH) dose for dogs?
For dogs, Isoniazid (INH) is typically dosed as follows — Used for M: 10–20 mg/kg PO q24h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Isoniazid (INH) dose for cats?
For cats, Isoniazid (INH) is typically dosed as follows — M: 10–15 mg/kg PO q24h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›Does Isoniazid (INH) need a prescription?
Yes. Isoniazid (INH) is a prescription medication and should only be administered under veterinary supervision.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →